This present invention is directed to a damping apparatus for a bicycle fork, more particularly to a leg portion of a bicycle fork that provides both compression and rebound damping. Most particularly, the present invention relates to a leg portion of a bicycle fork that includes dual pistons that are individually adjustable to control the compression and rebound functions of the fork leg.
Conventional bicycle forks connect a front wheel of a bicycle to a bicycle frame so that the rider can rotate the front wheel and steer the bicycle. The bicycle fork typically includes a fork steerer tube that is easily rotated by handlebars. The steerer tube is coupled to a fork crown that extends across the top of the bicycle wheel. Two blades extend from opposing ends of the fork crown on opposite sides of the wheel to securely attach the crown to opposite sides of an axle of the front bicycle wheel.
Bicycle forks are not only used to steer bicycles, but they are also used to absorb various loads that are experienced by a front wheel of the bicycles. See, for example U.S. Pat. No. 5,445,401 to Bradbury. These conventional bicycle forks are known to include inner and outer telescoping members that are compressible toward one another and expandable away from one another to absorb shock.
In rough terrain, however, these telescoping bicycle forks often rebound too rapidly after hitting a large bump. Some bicycle riders have also found that traditional telescoping bicycle forks compress too rapidly upon hitting small bumps. Therefore, manufacturers of bicycle forks have developed damping apparatuses that have damping mechanisms for controlling the relative movement between the telescoping members. See, for example U.S. Pat. No. 5,445,401. Although bicycle riders have embraced damping bicycle forks, as riders maneuver their bicycles over rougher terrain for longer lengths of time heat build-up within the damping fluid can cause some traditional forks to "seize" due to pressure buildup in a closed system. This undesirable result has led some riders to use a damping apparatus that allows the damping oil to freely circulate between the two telescoping legs. Such an apparatus, however adds unnecessary weight to the bicycle and is difficult to dissemble. What is needed is a damping apparatus that is incorporated into a bicycle fork that provides individual compression damping and rebound damping. The damping apparatus of the present invention is capable of permitting expansion of the fluid therein during heat buildup caused by hard riding on rough terrain, is lightweight, is self-contained within a leg of the bicycle fork, and permits disassembly and internal tuning or replacement of damping mechanism without draining damping fluid for easy maintenance. The damping apparatus of the present invention includes an oil cartridge whose level can change the spring characteristics of the fork. The damping apparatus of the present invention can be adjusted so that the compression and rebound of the fork can easily changed to suit the needs of the person riding on the bicycle.
According to the present invention, a damping apparatus is provided for use in a bicycle fork. The damping apparatus comprises first and second cylinders that are telescoped together, a compression piston located in the first cylinder, and a rebound piston reciprocally disposed in the first cylinder and fixed relative to the second cylinder. In addition, the compression and rebound pistons define between themselves a variable zone in the first cylinder. The rebound piston defines a rebound zone between the lower end of the first cylinder and the rebound piston. Further, fluid in the variable zone moves from the variable zone into the compression zone and into the rebound zone when the rebound piston moves toward the compression piston and moves into the variable zone when the rebound piston moves away from the compression piston. The pistons provide for flow of fluid between the zones.
According to another embodiment of the present invention a damping apparatus is provided for use in a bicycle fork. The damping apparatus comprises a lower cylinder that includes an upper end and a lower end, an upper cylinder that has an upper end and a lower end telescopically received in the lower cylinder, a compression piston located in the upper cylinder to divide the upper cylinder into an upper compression zone and a lower zone, and a rebound piston reciprocally disposed in the upper cylinder and fixed relative to the lower cylinder. The compression and rebound pistons define between themselves a variable zone in the upper cylinder. Further, the rebound piston defines a rebound zone between the lower end of the upper cylinder and the rebound piston. Fluid in the variable zone is moved from the variable zone into the compression zone and the rebound zone when the rebound piston moves toward the compression piston and moves into the variable zone when the rebound piston moves away from the compression piston. The pistons include passages for flow of fluid between the zones.
In yet another embodiment of the present invention, a damping apparatus for use in a bicycle fork is provided. The damping apparatus includes a lower leg that has a top end with a rim, a bottom end, and a chamber that extends between the ends, an upper leg that has an outer end, an inner end that is sized to extend through the rim and into the chamber, and a center portion that defines a cavity that extends between the ends, and fluid situated within the upper leg. In addition, a compression piston unit is positioned within the cavity of the upper leg. The compression piston unit includes a compression coupler with an oil flow aperture, a compression piston that is mounted on the coupler, engages the center portion of the upper leg, and has apertures therethrough, a shim that engages the piston, and blow-off valve means that selectively permits fluid flow through the apertures in the piston. A rebound piston unit is also positioned within the cavity of the upper leg. The rebound unit includes a hollow rebound shaft that has a first end coupled to the bottom end of the lower leg and an opposite end situated within the cavity, a rebound coupler mounted on the opposite end of the shaft, a slotted rebound piston mounted on the coupler, a shim that engages the piston, and blow-off valve means for selectively permitting fluid flow through the slots. In addition, a compression adjustment mechanism is selectively coupled to the compression piston unit and a rebound adjustment mechanism selectively coupled to the rebound piston unit. The compression adjustment mechanism includes means for adjusting the diameter of the oil flow aperture through the coupler of the compression piston unit and the rebound adjustment mechanism includes means for adjusting the diameter of the oil flow aperture through the coupler of the rebound piston unit.
Beneficially, the damping apparatus of the present invention provides separately controlled compression and rebound damping mechanisms. Oil is situated in an upper leg of the bicycle fork. Compression damping is achieved by passing the oil through the compression piston via the coupler. The oil is free to rise within the upper leg due to displacement of the shaft and the cartridge not being fixedly sealed. This system can work on an emulsion type or it can also have a floating piston with a pressurized chamber to eliminate emulsion. On the compression stroke, the rebound piston mechanism has a blow-off valve to eliminate a vacuum effect and to minimize the effect of the rebound piston mechanism on the compression damping. When the fork reverses from compression to rebound, the compression piston has a blow-off valve which allows the oil to transfer back into the main chamber as the rebound mechanism travels out of the upper leg. Rebound damping is achieved by oil transferring from one side of a rebound piston to the other, via a coupler. Due to having two separate pistons, couplers, and shim stacks, along with individual blow-off valves, it gives the bicycle rider the opportunity to have individual compression and rebound external adjustments that have minimal effect on the opposite circuit.
It has been found that a damping apparatus that has two opposing pistons with individual blow-off valves provides users of a suspension bicycle fork that has individually adjustable compression damping and rebound damping settings. Beneficially, a bicycle rider can adjust the damping apparatus to accommodate their personal riding preferences, or to adjust to changing trail terrain.
Additional objects, features, and advantages of the present invention will become apparent to those skilled in the art upon consideration of the following detailed description of preferred embodiments exemplifying the best mode of carrying out the invention as presently perceived.